On the one hand, the invention relates to a device for actuating binding and tension warp yarns, comprising at least one first shed forming device for actuating the tension warp yarns, and at least one second shed forming device for actuating the binding warp yarns. On the other hand, the invention relates to a pile weaving machine, preferably a face-to-face weaving machine, provided with such a device.
On a pile weaving machine, one or several backing fabrics are woven, in which pile warp yarns are used and interlaced in order to form pile loops or a cut pile.
When the pile weaving machine is a face-to-face weaving machine, an upper and a lower backing fabric are woven simultaneously between which pile warp yarns may extend connecting both fabrics to one another, and in which, after having cut the said pile warp yarns, two pile fabrics are obtained, i.e. a lower fabric and an upper fabric. In each of the two backing fabrics, pile warp yarns may be interlaced separately, either directly around the wefts, or by means of spacers in order to obtain pile loops. Thus, cut pile fabrics, as well as loop fabrics, false loop fabrics or combinations of these fabrics may be woven. In both fabrics binding and tension warp yarns, of which yarns are usually found in each warp system, are forming the backing fabric, together with the weft yarns.
In the (backing) fabric, the binding and tension warp yarns each have a different function.
The binding warp yarns are having the following functions:                Tying up the weft yarns in the backing fabrics, the binding warp yarns enveloping the wefts which have been inserted into the fabric and regularly crossing those wefts in order alternately to extend above and below the wefts in this manner. The path of the binding warp yarns and the way they are crossing will determine how many shots (how many wefts) per unit of length will be inserted into the fabric, the basic rule being that the more crossings are effected by the binding warp yarns, the less tight the fabric will be, because the binding warp yarns crossing will reduce the place of the weft yarns in order to beat them up tightly.        Supporting the rapiers. In rapier weaving machines, and therefore also in a face-to-face weaving machines with one or several rapier systems, the carrier and the gripper rapier, in their course towards one another in order to take over the weft yarn, have to be supported. To that effect, a yarn layer is formed in the shed right below the path of the rapier. To this effect, the binding warp yarns may be used.        In a three rapier weaving machine, the binding warp yarns have to be positioned in three positions.                    in the upper fabric above the upper rapier, between the upper rapier and the middlemost rapier, between the middlemost rapier and the lower rapier;            in the lower fabric below the lower rapier, between the lower rapier and the middlemost rapier, between the middlemost rapier and the upper rapier;                        These three positions are required both for tying up also the middlemost weft and to avoid that the upper and the lower fabric will get interwoven. The third position is also of importance in order to enable the rapiers to perform their supporting function.        
The tension warp yarns have the following functions:                to separate the wefts inserted into two layers in the backing fabric (wefts situated above the tension warp yarn and wefts situated below the tension warp yarn). This effect is realized by putting a higher strain on the tension warp yarns than on the binding warp yarns.        preventing the pile warp yarn from crossing or spreading those crossings as much as possible during the period the shed is being formed (=motion of all warp yarns in order to take up their positions to be able to realize the fabric desired with the weave and pattern as requested at the next weft insertion). The tension warp yarn is under a higher strain than the binding warp yarn, and therefore it will usually also have a larger cross-section. When the warp yarns are positioning themselves during the period the shed is being formed, yarns may get crossed. With such a crossing, a considerable number of warp yarns are situated next to one another, what, with large numbers of rather thicker warp yarns (for instance, pile warp yarns and tension warp yarns) may give cause to high friction, yarn breakage and of yarns getting entangled. Therefore, the various packages of warp yarns (pile, tension and binding warp yarns) are kept apart as much as possible and the number of warp yarns crossing simultaneously, is kept as low as possible and the warp yarns with the greatest diameter will be spared as much as possible in doing so;        This problem may be solved by:                    causing the motion of the backing warp yarns to pass off out of phase with respect to the motion of the pile warp yarns;            causing certain warp yarns, for instance the tension warp yarns to move further on than other warp yarns, for instance the pile warp yarns, in order to avoid certain crossings entirely in this manner;            splitting up the weaving frames, for instance those of the tension warp yarns, causing a necessary crossing, for instance, with the pile warp yarns, to be divided between two groups, because of which a crossing may be realized at different times, by means of a different law of motion.                        Pulling open the face-to-face fabric within the height of the jaw, thus maintaining the pile height at a constant value. This function is mainly of importance when weaving with three rapier weaving, because with this method the use of lancets as spacers between the upper and the lower fabric is not possible. In this case, the tension warp yarn is used in order to take over this function. Also with double rapier weaving, it may be necessary to decide to weave without using lancets because of economic or technical reasons and in this case also, the tension warp yarns should ensure the distance between the upper and lower fabric by means of their tension.        Supporting the rapiers. Preferably, the tension warp yarns are used to that effect, because the higher tension of the yarns will provide a better guiding of the rapiers along the supporting layer. Only, the tension warp yarns are not always available for this supporting function, because of their other functions, among which avoiding and spreading crossings with the pile warp yarns or their positioning above the rapier. It may also be advantageous to split the tension warp yarns into a portion having a supporting function for the rapiers and a portion positioning themselves further away from the rapiers, out of reach of the pile warp yarns.        
When developing and producing new textures, a strong emphasis is lying on fabrics with a higher density and a better quality. The methods here applied are expected to enable to shift from one fabric to another in a flexible manner and with minimal transformations of the machine. These minimal transformations have to be as controllable as possible from the controls of the machine without any mechanical means and mechanical conversion.
In order to produce fabrics with a higher density, the density has to be increased, both in the weft direction, i.e. more warp yarns per unit of length, and in the warp direction, i.e. more wefts per unit of length. A higher density in the weft direction will have the effect that the mass of warp yarns causing crossings of warp yarns will become tighter, and therefore crossings should be more avoided or should be more spread out. A higher density in the warp direction has the effect that it is necessary to deal with binding warp yarns in a creative way in order to minimize the number of crossings and yet to obtain a good or even better quality of the fabric. The quality of the fabric is namely determined by the purity of the back, pile strength, whether a pile is standing upright or not, if not any other effect is purposely aimed at, and the form retention of a fabric in which also the weft yarns should be well stuck.
The flexibility in the methods applied mainly consists in actuating, from the control of the machine, changes in the nature of the pile forming, but also in carrying out the backing weave, in other words in the manner in which the binding and tension warp yarns are moving through several cycles. These actions taken on the machine control may occur both by means of a manual interaction of the operator of the machine and by completing a programme with which several fabrics with a variety of textures may be woven successively. Realising these aims will be strongly determined to the extent in which the binding and tension warp yarns of the backing fabric may be flexibly actuated.
To actuate the binding and tension warp yarns of the backing fabrics during pile weaving, it has been customary for quite some time, to use cam disc machines, one drive driving a series of cams, each cam driving a weaving frame, which is positioning a set of warp yarns in order to take up their position in the geometry of the shed. This solution has the disadvantage that, on the one hand the number of weaving fames being driven in this manner, will be limited to eight and that a change of the texture for the backing weave usually requires the cams to be exchanged. Optimization of crossings and geometry of the shed will occur by exchanging the cams or by adjusting the cams on the central drive shaft. Both changes are rather time-consuming and will prevent a flexible shifting from one texture to another.
With the changeover to electronic dobby devices, where the required position may be passed and selected at each shot, a higher flexibility has been obtained in the field of textures. However, with respect to an optimal forming of the shed, there is not a single possibility left to spread the motional evolution of warp yarns driven by the same dobby device. Moreover, a dobby device is able to absorb only more limited forces than the cam disc machines. Hence, that dobby devices, as far as pile weaving is concerned, were initially used mainly for velvet weaving, and only later on they were introduced for carpet weaving. Besides the disadvantages in order to obtain an optimal shed forming, this method to form the shed is indeed enabling a larger variety of weaves. The effect of strong forces which has to be controlled with large weaving widths and great strains in the warp yarns is imposing limits. The heavy and expensive dobby systems used to that effect with carpet weaving, are further limited to a maximum of twelve weaving frames. Moreover, no applications are known where this kind of shed forming device is used for weaving backing warp yarns on weaving machines provided with three rapiers, simultaneously inserting a weft. In this case a dobby system would have to position each binding warp yarn in three positions. Thinking in terms of the devices known, such a construction is in principle easy to produce. However, because of this, the number of weaving frames available for the backing weave is still further restricted, as per weaving frame, two selection elements are required in order to realize the three positions.
In EP 848 097 a solution is described where weaving frames are provided for driving the tension and binding warp yarns, which each are driven by a separate motor, the driving chain between the motor and the weaving frame is passing a first lever driving the weaving frame through an intermediate drive. The purpose of the invention being to obtain an increase of the flexibility, to optimize the geometry of the shed and to improve the laws of motion. However, providing one motor for each weaving frame as a solution is also an expensive solution. Furthermore, the tension and binding warp yarns each will still be driven by a motor which will indeed be able to realize a different law of motion, but which, in all cases, is driving a weaving frame. The number of weaving frames, that may be installed one after the other will, for practical reasons, still be limited to twelve, because in case more weaving frames will be used, the extreme positions into which should be taken the backing warp yarns, the farthest from the weaver, will be situated too far away from one another to be able to realize shed forming means. This problem will claim the attention even more with face-to-face weaving machines with three rapiers, where the binding warp yarns should be able to move from a position situated above one rapier into a position situated below the lower rapier and to that effect should be able to perform a greater motion than with a weaving machine where two rapiers are simultaneously inserting one weft into the backing fabrics.
In EP 1 180 556 methods are represented and described for manufacturing fabrics having a high density and a high quality, however, how the tension and binding warp yarns are driven in order to realize these textures has not been indicated.
In the state-of-the-art described in U.S. Pat. No. 6,186,186 it is suggested that up to three Jacquard devices are used on one face-to-face weaving machine for weaving face-to-face pile fabrics, two Jacquard devices of which are used for positioning backing warp yarns in the shed. The splitting up here performed, however, is not the splitting up between binding and tension warp yarns in order to be able to make a better use of the various functions of the types of yarn, but it is a splitting up between a two-position Jacquard machine for the backing warp yarns of the upper fabric and a two-position Jacquard machine for the backing warp yarns of the lower fabric, in order to realize a backing effect in both fabrics between warp yarns and weft yarns in the areas where now cut pile occurs.